Much present day electronic equipment requires carefully regulated power including currents and voltages which must be controlled within a high degree of accuracy to specific values. More particularly, modern high-speed electronic equipment is sensitive to relatively short transients or interruptions in power. Consequently, power supplies for such equipment must be able to respond quickly to transients in order to maintain proper regulation and avoid equipment damage. In order to supply regulated power to sensitive electronic equipment several different types of power supplies are now in current use.
One common type of power supply is a analog or series regulator in which an analog control element is inserted between an unregulated source of power and the equipment utilizing the power. Such a regulator is capable of supplying an accurate and stable power supply providing that the analog element can respond sufficiently fast to intercept transient conditions. A drawback of the analog supply is that a large amount of power is dissipated in the analog control element which results in a bulky and expensive assembly.
Another type of regulated power supply which is more efficient is called a "switching regulator". In such a power supply, the output or regulated voltage is controlled by intermittently and periodically connecting the unregulated voltage source through a filter circuit to the utilization equipment (by pulsing the input voltage). The output voltage is regulated by varying the time duration (modulating the width of the input pulse) during which the unregulated voltage is connected to the equipment.
A similar switching or pulse-width modulation arrangement is often used in DC-to-AC and DC-to-DC converters. In this type of circuit, the pulse width modulation circuit periodically connects the unregulated supply to a transformer which then transforms the pulse modulated input waveform to a desired voltage. The transformer output is then filtered to provide the final output voltage.
In order to provide good response time and small size with a switching power supply, it is necessary to operate the supply at a high frequency. However, in prior art circuits, the switching frequency has been limited by the conventional circuit arrangement. In particular, a switching power supply has five main components. The first component is an output transistor (or transistors) which connects the unregulated supply to the utilization device. The switching transistor is, in turn, controlled by another component, a latch circuit, which determines whether the transistor is "on" or "off" depending on whether the latch is "set" or "reset".
The latch is periodically set by an astable or free-running oscillator circuit which determines the frequency at which the supply operates. In order to control the width of the input pulse, the latch is reset after a time duration (thereby turning "off" the output transistor) by a comparator circuit (the fourth component).
The comparator compares an error signal which is derived from the output voltage to a ramp signal generated by the last component, a ramp generator. The ramp generator is triggered by the oscillator and develops an output signal which is a linearly increased voltage ramp. When the error voltage equals the ramp voltage, the comparator resets the latch and turns "off" the output transistor.
In accordance with the above circuitry, the latch (and subsequently the output transistor) is periodically set by the oscillator. The latch remains set for a period of time determined by the length of time taken by the ramp voltage to rise to the error voltage. If the output voltage decreases an error circuit increases the error voltage, thus causing the output transistor to remain "on" for a longer time. By varying the width of the pulses delivered to the utilization device, the circuit regulates the output voltage.
One problem with operating such a circuit at a high switching frequency is that several of the main elements are connected in series. In particular, the comparator is connected to the latch which is, in turn, connected to the output transistor. Each of these series-connected elements delays signals passing through it. Since the propagation delays add, the total delay can be sufficient to cause errors in performance of the circuit. Heretofore it has been possible to increase the switching frequency of such a circuit only by decreasing the propagation delays of the components. However, very high-speed components are expensive and consume more power than their slower counterparts.
It is accordingly an object of the present invention to provide a switching regulator which can be operated at higher frequencies than conventional regulators.
It is another object of the present invention to provide a switching regulator in which the series connection of the control elements is eliminated.
It is still another object of the present invention to increase the switching frequency of a switching regulator while utilizing presently available components.
It is a further object of the present invention to provide a switching regulator which does not use specialized components but can be built with standard readily available electronic circuits.
It is yet a further object of the present invention to provide a switching regulator which simplifies the circuitry by eliminating some of the prior art components.